Forward osmosis has been used for desalination. In general, a forward osmosis desalination process involves a container having two chambers separated by a semi-permeable membrane. One chamber contains seawater. The other chamber contains a concentrated solution that generates a concentration gradient between the seawater and the concentrated solution. This gradient draws water from the seawater across the membrane, which selectively permits water to pass, but not salts, into the concentrated solution. Gradually, the water entering the concentrated solution dilutes the solution. The solutes are then removed from the dilute solution to generate potable water.
There are a variety of issues that can arise with respect to the feed solutions supplied to the forward osmosis process. For example, the feed solution can have a sufficiently low salinity that the concentrated draw solution on the opposite side of the membrane becomes highly diluted by the process, thereby complicating the recovery/regeneration of the draw solution. The condition of the feed solution may also require the use of certain pretreatment processes to make it usable in the forward osmosis process. Most pretreatment processes make the overall process more costly by, for example, requiring the use of additional energy or chemicals (e.g., lime softening) or further steps (e.g., regeneration of an ion exchange resin). Additionally, there can be disposal issues with the concentrated feed solution after forward osmosis processing. For example, highly concentrated brine raises environmental disposal issues, e.g., discharging concentrated brine into a body of water negatively impacts the local ecosystem. While there are some solutions for these problems, they tend to be expensive and/or add undue complexity to the basic forward osmosis process.